/dev/sd[a,b][0-9] --> root (/dev/sd[a,b][0-9]) # simple... if only "root=" in /proc/cmdline.
/dev/sd[a,b][0-9] --> lvm2 (/dev/mapper/*)--> root (/dev/mapper/*-root) # root on lvm2. if only "lvm_dev=" "root=" in /proc/cmdline.
/dev/sd[a,b][0-9] --> dmcrypt (/dev/sd[a,b][0-9]) --> root (/dev/sd[a,b][0-9]) # root on encrypted partishion. if "dmcrypt_dev=" "root=" in /proc/cmdline
/dev/sd[a,b][0-9] --> dmcrypt (/dev/sd[a,b][0-9]) --> lvm2 (/dev/mapper/*)--> root (/dev/mapper/*-root) # root on lvm2 over encrypted partishion. if "dmcrypt_dev=" and "lvm_dev=" "root=" in /proc/cmdline.
/dev/sd[a,b][0-9] --> raid-1 (/dev/md[0-9])--> root (/dev/md[0-9]) # root in raid. if only "mdadm_dev=" "root=" in /proc/cmdline.
/dev/sd[a,b][0-9] --> raid-1 (/dev/md[0-9])--> lvm2 (/dev/mapper/*)--> root (/dev/mapper/*-root) # root on lvm2 in raid. if "mdadm_dev=" "lvm_dev=" "root=" in /proc/cmdline.
/dev/sd[a,b][0-9] --> raid-1 (/dev/md[0-9])--> dmcrypt (/dev/md[0-9]) --> root (/dev/md[0-9]) # root on encrypted partishion in raid. if "mdadm_dev=" "dmcrypt_dev=" "root=" in /proc/cmdline
/dev/sd[a,b][0-9] --> raid-1 (/dev/md[0-9])--> dmcrypt (/dev/md[0-9]) --> lvm2 (/dev/mapper/*)--> root (/dev/mapper/*-root) # root on lvm2 over encrypted partishion in raid. if "mdadm_dev=" "dmcrypt_dev=" "lvm_dev=" "root=" in /proc/cmdline.